Method for converting waste plastics into natural gas through tandem catalysis
Through a two-stage tandem catalytic method, the waste plastic is pyrolyzed into CO, CO2, C1-C6, H2 and other products in the first stage, and then converted into methane-rich natural gas in the second stage, solving the problems of low conversion efficiency of waste plastics and catalyst deactivation, and achieving efficient resource utilization.
Patent Information
- Application Number
- CN202510626780.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-15
- Publication Date
- 2025-08-15
AI Technical Summary
The prior art is difficult to efficiently convert waste plastic into natural gas, and there are problems of tar formation and catalyst deactivation.
Using a two-stage tandem catalytic method, first a pyrolysis reaction is carried out in the first sealed reactor, and molecular sieve, nickel-containing oxide or calcium-containing oxide is used as a pyrolysis catalyst to convert the waste plastic into CO, CO2, C1-C6, H2 and other pyrolysis products. Then, layered metal hydroxides or perovskite oxides are used as reforming catalysts in the second sealed reactor to convert these products into methane-rich natural gas.
The efficient conversion of waste plastics into methane-rich natural gas is achieved, the resource utilization rate is improved, the tar generation and catalyst sintering are inhibited, and the conversion efficiency is improved.
Smart Images
Figure CN120484861A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of solid waste resource utilization, and in particular to a method for converting waste plastics into natural gas through series catalysis. Background Art
[0002] With rapid economic development, people's dependence on plastic products is increasing. However, plastics have a short lifespan and low recycling rates. Large amounts of untreated plastic waste are not properly managed and remain in the natural environment, posing a serious threat to ecosystems and humanity. Current plastic production relies on fossil fuels, and greenhouse gas emissions from the entire plastic lifecycle are projected to increase to 6.5 billion tons of carbon dioxide equivalent by 2050. Therefore, the environmental and climate change issues caused by plastic waste require urgent resolution.
[0003] Currently, the primary method for recycling waste plastics is incineration for power generation, but this process emits significant amounts of CO₂. Furthermore, the acidic gases and polycyclic aromatic hydrocarbons (PAHs) produced during incineration can cause secondary pollution. Pyrolysis technology offers the greatest potential for chemically recycling waste plastics, but the products are widely distributed and of poor quality. Coupled catalytic technology can significantly improve reaction efficiency and product selectivity. Chemically, the largest proportion of waste plastics is comprised of polyolefins such as polyethylene (PE), polypropylene (PP), and polystyrene (PS), as well as polyethylene terephthalate (PET), which contain high levels of carbon and hydrogen. Reports suggest that waste plastics can be converted into hydrogen through catalytic cracking, but hydrogen storage and transportation systems are still immature, and this technology approach has a low carbon utilization rate. From an atom economy perspective, converting waste plastics into natural gas, primarily composed of CH₄, maximizes the utilization of carbon and hydrogen. Furthermore, as a major energy source, natural gas has a mature pipeline network and downstream market, giving this technology a natural advantage.
[0004] Therefore, providing a method for converting waste plastics into natural gas through tandem catalysis is of great practical significance. Summary of the Invention
[0005] The object of the present invention is to provide a method for converting waste plastics into natural gas through series catalysis in order to overcome the deficiencies of the prior art.
[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:
[0007] The present invention provides a method for converting waste plastics into natural gas through series catalysis, comprising the following steps:
[0008] 1) waste plastics and a pyrolysis catalyst are mixed in a first-stage closed reactor and then subjected to pyrolysis reaction to obtain pyrolysis products;
[0009] 2) The pyrolysis products enter the second-stage closed reactor, react under the reforming catalyst, and are converted into natural gas.
[0010] Preferably, the waste plastics in step 1) include one or more of polyethylene, polypropylene, polystyrene and polyethylene terephthalate; and the particle size of the waste plastics is ≤5 mm.
[0011] Preferably, the pyrolysis catalyst in step 1) is one or more of a molecular sieve, a nickel-containing oxide and a calcium-containing oxide.
[0012] Preferably, in step 1), the mass ratio of the waste plastic to the pyrolysis catalyst is 0.3-1:1-3.
[0013] Preferably, the temperature of the pyrolysis reaction in step 1) is 300-700°C; the pyrolysis products are CO, CO2, C1-C6, H2 and a small amount of pyrolysis oil.
[0014] Preferably, in step 2), the reforming catalyst is a layered metal hydroxide derived by in situ reduction, a perovskite oxide derived by in situ reduction, or a supported catalyst, and the layered metal hydroxide is a layered double metal hydroxide or a layered triple metal hydroxide; in the supported catalyst, the active component is Ni, and the carrier is one or more of molecular sieves, alumina, yttrium oxide, and lanthanum oxide.
[0015] Preferably, the mass ratio of the waste plastic in step 1) to the reforming catalyst in step 2) is 0.3-1:0.2-1.
[0016] Preferably, the reaction temperature in step 2) is 250-400°C.
[0017] Preferably, the pyrolysis reaction in step 1) and the reaction in step 2) are carried out in a protective atmosphere, which is one or more of nitrogen, argon and helium.
[0018] The beneficial effects of the present invention include the following:
[0019] 1) The present invention provides a method for converting waste plastics into natural gas through series catalysis, namely, a catalytic pyrolysis and catalytic reforming method: a two-stage closed reactor, a first-stage closed reactor and a second-stage closed reactor are connected, a pyrolysis catalyst and waste plastics are placed in the first-stage closed reactor for mixing and fully pyrolysis, and a reforming catalyst is placed in the second-stage closed reactor. The pyrolysis products produced in the first-stage closed reactor are passed into the second-stage closed reactor and converted into natural gas under the action of the reforming catalyst.
[0020] 2) The present invention utilizes tandem catalytic technology to pyrolyze waste plastics to a high degree in a first-stage closed reactor into pyrolysis products primarily containing CO, CO2, C1-C6, and H2. In a second-stage closed reactor, CO and CO2 are hydrogenated and reduced to CH4, while C1-C6 is deeply pyrolyzed into CH4. The method of the present invention converts waste plastics into methane-rich natural gas, realizing resource utilization of waste plastics and representing an effective carbon reduction technology. The method of the present invention achieves low-carbon, high-value, and high-quality resource utilization of waste plastics. Furthermore, the use of a catalyst with a specially structured structure effectively suppresses tar formation, catalyst sintering, and deactivation due to carbon deposition, thereby improving the efficiency of the conversion of waste plastics to natural gas. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 Schematic diagram of the flow of materials in a two-stage connected closed reactor of the present invention. DETAILED DESCRIPTION
[0022] The present invention provides a method for converting waste plastics into natural gas through series catalysis, comprising the following steps:
[0023] 1) waste plastics and a pyrolysis catalyst are mixed in a first-stage closed reactor and then subjected to pyrolysis reaction to obtain pyrolysis products;
[0024] 2) The pyrolysis products enter the second-stage closed reactor, react under the reforming catalyst, and are converted into natural gas.
[0025] In the present invention, the waste plastic in step 1) preferably comprises one or more of polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET); the particle size of the waste plastic is preferably ≤5 mm, more preferably ≤4 mm, and more preferably ≤3 mm.
[0026] In the present invention, the pyrolysis catalyst in step 1) is preferably one or more of a molecular sieve, a nickel-containing oxide, and a calcium-containing oxide.
[0027] In the present invention, the mass ratio of the waste plastics to the pyrolysis catalyst in step 1) is preferably 0.3-1:1-3, more preferably 0.5-0.8:1.2-2.6, and more preferably 0.6-0.7:1.5-2.5.
[0028] In the present invention, the temperature of the pyrolysis reaction in step 1) is preferably 300-700°C, more preferably 400-600°C, and more preferably 500°C; the pyrolysis products are preferably CO, CO2, C1-C6, H2 and a small amount of pyrolysis oil.
[0029] In the present invention, the reforming catalyst in step 2) is preferably derived from a layered metal hydroxide by in-situ reduction, derived from a perovskite oxide by in-situ reduction, or a supported catalyst, and the layered metal hydroxide is preferably a layered double metal hydroxide or a layered triple metal hydroxide; the layered metal hydroxide and the perovskite oxide are preferably prepared by a hydrothermal method, a coprecipitation method, a sol-gel method, a lemon thermal combustion method, or a condensation reflux method; in the supported catalyst, the active component is preferably Ni, the carrier is preferably one or more of molecular sieves, alumina, yttrium oxide, and lanthanum oxide, and the supported catalyst is preferably prepared by an impregnation method.
[0030] In the present invention, the mass ratio of the waste plastic in step 1) to the reforming catalyst in step 2) is preferably 0.3-1:0.2-1, more preferably 0.4-0.9:0.3-0.8, and even more preferably 0.5-0.8:0.5-0.6.
[0031] In the present invention, the reaction temperature in step 2) is preferably 250-400°C, more preferably 280-350°C, and even more preferably 300-320°C.
[0032] In the present invention, the pyrolysis reaction in step 1) and the reaction in step 2) are preferably carried out in a protective atmosphere, and the protective atmosphere is preferably one or more of nitrogen, argon and helium.
[0033] The flow diagram of the material in the two-stage closed reactor of the present invention is as follows Figure 1 shown.
[0034] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0035] In the embodiment, a two-stage closed reactor is used, wherein the first stage closed reactor is a pyrolysis stage, and the second stage closed reactor is a quality-improving stage.
[0036] Example 1
[0037] 3 mL of nickel nitrate aqueous solution containing 0.2 g of Ni was added dropwise to 1 g of Y2O3 support at a rate of 1 mL / min to fully wet it. After drying in an oven at 105°C, it was transferred to a muffle furnace and calcined at 500°C for 5 h, and then reduced at 500°C for 2 h in a H2 atmosphere to prepare a Ni / Y2O3 catalyst.
[0038] First, 0.3g Ni / Y2O3 catalyst was placed in the upgrading section and heated to 300℃ in a nitrogen atmosphere. Then, 1g PE and PP (the particle size of PE and PP were both 3mm) with a mass ratio of 1:1 and 1g MCM-22 molecular sieve were placed in the pyrolysis section and mixed evenly. The pyrolysis section was heated to 700℃ at a rate of 10℃ / min in a nitrogen atmosphere. At the same time, the generated pyrolysis products were passed into the upgrading section. The residence time of the raw materials in the pyrolysis section was 70min, and the residence time of the catalyst in the upgrading section was 80min. Natural gas was collected at the outlet of the upgrading section.
[0039] The yield of natural gas obtained in this embodiment is 610 mg, wherein the mass content of methane is 86.2%, the mass content of H2 is 5.8%, and the mass content of C2-C6 is 6.5%.
[0040] Example 2
[0041] Nickel nitrate and yttrium nitrate with a molar ratio of 75:25 were dissolved in 500 mL of deionized water, and then urea with a molar ratio of 10 times the metal was added and stirred thoroughly to dissolve. The mixture was then transferred to a condensation reflux device and heated at 95 ° C for 8 h. After cooling, the precipitate was filtered, washed with deionized water and anhydrous ethanol in sequence, and dried to obtain layered Ni 75 Y 25 O x The oxides were reduced at 500 °C for 2 h in H2 atmosphere before the catalytic reaction.
[0042] First, 0.4 g of in-situ reduced layered Ni 75 Y 25 O x The catalyst was placed in the upgrading section and heated to 320°C in a nitrogen atmosphere. Then, 1g of PE and PP (the particle size of both PE and PP was 3mm) with a mass ratio of 1:1 and 1g of FER type β molecular sieve were placed in the pyrolysis section and mixed evenly. The pyrolysis section was heated to 700°C at a rate of 10°C / min in a nitrogen atmosphere. At the same time, the generated pyrolysis products were passed into the upgrading section. The residence time of the raw materials in the pyrolysis section was 70min, and the residence time of the catalyst in the upgrading section was 90min. Natural gas was collected at the outlet of the upgrading section.
[0043] The yield of natural gas obtained in this embodiment is 530 mg, wherein the mass content of methane is 85.2%, the mass content of H2 is 7.9%, and the mass content of C2-C6 is 5.6%.
[0044] Example 3
[0045] Nickel nitrate, aluminum nitrate, and yttrium nitrate in a molar ratio of 75:24:1 were dissolved in 500 mL of deionized water, followed by the addition of urea at a 10-fold metal molar ratio and sufficient stirring to dissolve. The solution was then transferred to a condensation reflux device and heated at 95°C for 8 hours. After cooling, the resulting precipitate was filtered, washed with deionized water and anhydrous ethanol, and dried to obtain layered Ni 75 Al 24 Y1O x The oxides were reduced at 500 °C for 2 h in H2 atmosphere before the catalytic reaction.
[0046] First, 0.5g of in-situ reduced layered Ni 75 Al 24 Y1O x The catalyst was placed in the upgrading section and heated to 350°C in a nitrogen atmosphere. 0.3g of PET with a particle size of 3mm and 2.6g of Ni2O3 were then placed in the pyrolysis section and mixed evenly. The pyrolysis section was heated to 600°C at a rate of 10°C / min in a nitrogen atmosphere. At the same time, the generated pyrolysis products were passed into the upgrading section. The residence time of the raw materials in the pyrolysis section was 60min, and the residence time of the catalyst in the upgrading section was 70min. Natural gas was collected at the outlet of the upgrading section.
[0047] The yield of natural gas obtained in this embodiment is 153 mg, wherein the mass content of methane is 82%, the mass content of H2 is 6%, and the mass content of C2-C6 is 2%.
[0048] Example 4
[0049] Nickel nitrate and aluminum nitrate with a molar ratio of 75:25 were dissolved in 500 mL of deionized water, and then urea with a molar ratio of 10 times the metal was added and stirred thoroughly to dissolve. Then the solution was transferred to a condensation reflux device and heated at 95 ° C for 8 hours. After cooling, the precipitate was filtered, washed with deionized water and anhydrous ethanol in sequence, and dried to obtain layered Ni 75 Al 25 O x The oxides were reduced at 500 °C for 2 h in H2 atmosphere before the catalytic reaction.
[0050] First, 0.3 g of in-situ reduced layered Ni 75 Al 25 O xThe catalyst was placed in the upgrading section and heated to 250°C in a nitrogen atmosphere. Then, 0.3g of PET with a particle size of 3mm, 0.65g of Ni2O3 and 0.58g of Ca(OH)2 were placed in the pyrolysis section and mixed evenly. The pyrolysis section was heated to 600°C at a rate of 10°C / min in a nitrogen atmosphere. At the same time, the generated pyrolysis products were passed into the upgrading section. The residence time of the raw materials in the pyrolysis section was 60min, and the residence time of the catalyst in the upgrading section was 80min. Natural gas was collected at the outlet of the upgrading section.
[0051] The yield of natural gas obtained in this embodiment is 158 mg, wherein the mass content of methane is 81%, the mass content of H2 is 16%, and the mass content of C2-C6 is 1.5%.
[0052] Example 5
[0053] Lanthanum nitrate and nickel nitrate at a molar ratio of 1:1 were dissolved in 500 mL of deionized water. Then, citric acid at a molar ratio of 1.2 times the metal ratio was added and stirred thoroughly to dissolve. The temperature was then raised to 100°C and stirred continuously until a sol was formed. After drying in an oven at 105°C, the resulting solid was ground into powder and transferred to a muffle furnace and calcined at 900°C for 5 h to produce LaNiO. x The oxides were reduced at 500 °C for 2 h in H2 atmosphere before the catalytic reaction.
[0054] First, 0.5g of in-situ reduced LaNiO x The catalyst was placed in the upgrading section and heated to 300°C in a nitrogen atmosphere. 0.1g PET, 0.2g PS (the particle size of PET and PS was 3mm) and 3g Ni2O3 were then placed in the pyrolysis section and mixed evenly. The pyrolysis section was heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. At the same time, the generated pyrolysis products were passed into the upgrading section. The residence time of the raw materials in the pyrolysis section was 50min, and the residence time of the catalyst in the upgrading section was 90min. Natural gas was collected at the outlet of the upgrading section.
[0055] The yield of natural gas obtained in this embodiment is 185 mg, wherein the mass content of methane is 84%, the mass content of H2 is 10.3%, and the mass content of C2-C6 is 2.8%.
[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.
Claims
1. A method for converting waste plastics into natural gas by tandem catalysis, characterized in that: The following steps are included: 1) waste plastics and a pyrolysis catalyst are mixed in a first-stage closed reactor and then subjected to pyrolysis reaction to obtain pyrolysis products; 2) The pyrolysis products enter the second-stage closed reactor, react under the reforming catalyst, and are converted into natural gas.
2. The method according to claim 1, characterized in that In step 1), the waste plastics include one or more of polyethylene, polypropylene, polystyrene and polyethylene terephthalate; and the particle size of the waste plastics is ≤5 mm.
3. The method according to claim 1 or 2, characterized in that In step 1), the pyrolysis catalyst is one or more of a molecular sieve, a nickel-containing oxide, and a calcium-containing oxide.
4. The method according to claim 3, characterized in that In step 1), the mass ratio of the waste plastic to the pyrolysis catalyst is 0.3-1:1-3.
5. The method according to claim 4, characterized in that Step 1) The temperature of the pyrolysis reaction is 300-700° C.; the pyrolysis products are CO, CO2, C1-C6, H2 and a small amount of pyrolysis oil.
6. The method according to claim 5, characterized in that Step 2) The reforming catalyst is derived from a layered metal hydroxide by in-situ reduction, derived from a perovskite oxide by in-situ reduction, or a supported catalyst, wherein the layered metal hydroxide is a layered double metal hydroxide or a layered triple metal hydroxide; in the supported catalyst, the active component is Ni, and the carrier is one or more of molecular sieves, alumina, yttrium oxide, and lanthanum oxide.
7. The method according to any one of claims 4 to 6, characterized in that: The mass ratio of the waste plastic in step 1) to the reforming catalyst in step 2) is 0.3-1:0.2-1.
8. The method according to claim 7, characterized in that Step 2) The reaction temperature is 250-400°C.
9. The method according to claim 8, characterized in that The pyrolysis reaction in step 1) and the reaction in step 2) are carried out in a protective atmosphere, wherein the protective atmosphere is one or more of nitrogen, argon and helium.